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From "Mamta A. Satoor (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-1478) Add built in language based ordering and like processing to Derby
Date Fri, 02 Feb 2007 21:51:05 GMT

    [ https://issues.apache.org/jira/browse/DERBY-1478?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12469885
] 

Mamta A. Satoor commented on DERBY-1478:
----------------------------------------

I have updated the functional spec based on some feedback from Dan. The changes to the spec
in brief are,
a)The collation ordering will apply only to CHAR and VARCHAR types 
2)The collation for system table will continue to be code point based no matter what collation
user chooses for CHAR and VARCHAR types. 
3)I will change the JDBC attribut to accept String values. This way, this feature can be expanded
in future to support more variety of collations rather than just the code point based ordering
and territory based ordering.

The functional spec now looks as follows
I would like to propose a way for supporting locale sensitive data in Derby. Currently, upto
Derby 10.2 release, the sorting for CHAR and VARCHAR data types is codepoint based (UNICODE).
For someone looking for any locale specific collation, they can possibly write a couple functions
as suggested by http://wiki.apache.org/db-derby/LanguageBasedOrdering, but that solution is
not complete and not efficient (since functional indexes can't be defined in Derby). 

My proposal for Derby 10.3 is that a user would be able to specify an optional JDBC url attribute,
called collation, at the database create time and that attribute can be set to one of the
following 2 values
1) UCS_BASIC (This means codepoint based collation. This will also be the default collation
used by Derby if no collation attribute is specified on the JDBC url at the database create
time. This collation is what Derby 10.2 and prior have supported) or 
2)TERRITORY_BASED_COLLATION (the collation will be based on language region specified by the
exisiting Derby attribute called territory (territory=ll_CC) http://db.apache.org/derby/docs/10.2/ref/rrefattrib56769.html
If the territory attribute is not specified at the database create time, Derby 10.2 uses java.util.Locale.getDefault
to determine the territory for the newly created database. Derby 10.3 will continue to use
the same mecahnism to determine the territory.)

The collation attribute will apply only for CHAR and VARCHAR datatypes defined in a user-defined
table. System tables will continue to use codepoint based collation for it's CHAR and VARCHAR
columns.

This collation ordering will impact operations that require returning the order of data on
CHAR and VARCHAR columns. That includes
1)Comparison using comparison operators (<, >, =, IN, BETWEEN)
2)Statements that involve sorting (ORDER BY, GROUP BY, DISTINCT, MAX, and MIN)
3)Statements that use the LIKE keyword

Derby already has lot of code for locale based ordering for disabled NATIONAL CHAR and NATIONAL
VARCHAR datatypes. I hope to leverage highly on that code and see how it can be used for this
project. Also, I am keeping a goal for myself to implement this in such a way that databases
with codepoint based collation will not get penalized by the code for locale based collation.

I am not planning to implement any new collation support on any existing database, ie JDBC
attribute collation will not be supported at the upgrade database time or on a pre-existing
database. Those databases will continue to use codepoint based collation. I am proposing to
implement the collation support only for new databases. 

Other than finding a means of storing the collation attribute from the JDBC url somewhere,
I don't anticipate any other disk changes as part of this project.

> Add built in language based ordering and like processing to Derby
> -----------------------------------------------------------------
>
>                 Key: DERBY-1478
>                 URL: https://issues.apache.org/jira/browse/DERBY-1478
>             Project: Derby
>          Issue Type: Improvement
>          Components: SQL
>    Affects Versions: 10.1.2.1
>            Reporter: Kathey Marsden
>         Assigned To: Mamta A. Satoor
>
> It would be good for Derby to have built in Language based ordering based on locale specific
Collator.
> Language based ordering is an important feature for international deployment.  DERBY-533
offers one implementation option for this but according to the discussion in that issue National
Character Types carry a fair amount of baggage with them especially in the form of concerns
about conversion   to and from datetime and number types. Rick  mentioned SQL language for
collations as an option for language based ordering. There may be other options too, but I
thought it worthwhile to add an issue for the high level functional concern, so the best choice
can be made for implementation without assuming that National Character Types is the only
solution.
> For possible 10.1 workaround and examples see:
> http://wiki.apache.org/db-derby/LanguageBasedOrdering

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